The disclosure relates to a shoe structure comprising an exterior upper, an interior upper, an insole and an outsole.
In shoes commercially available today, the interior upper consists in its simplest form of a single formed part whose ends are sewn together on the front side of the interior upper. As a result of this seam, the upper end of the interior upper and the lower sole-side end of the interior upper each form an opening, and the interior upper is given its form which follows the form of the upper material or the exterior upper. The seam runs roughly along the middle of the front interior upper area, i.e. along the middle of the forefoot and instep area, from the upper opening to the lower opening of the interior upper.
During the make-up of the shoe, the upper of the shoe which can comprise an interior upper and an exterior upper is drawn over a last and—depending on the design—lasted under the insole, i.e. is joined to the insole. As the prior-art one-piece interior upper has only a very limited stretchability along the seam that runs roughly along the middle of the front area of the interior upper from the upper to the lower interior upper opening, drawing of the interior upper over the last and subsequent lasting is extremely difficult or not possible at all.
As an alternative to one-piece interior uppers, a person skilled in the art will also be familiar with two-piece interior uppers which have a separate leaf in the front part of the interior upper that is joined to the interior upper by a seam which runs at right-angles to the forefoot area. A further alternative to the one-piece interior upper described is a two-piece interior upper with an insert that extends over the front area of the interior upper from the upper to the lower interior upper opening with the insert being joined to the interior upper by two lateral seams.
Although such two-piece interior upper constructions have the necessary stretchability in the front area of the interior upper and can therefore be easily drawn over the last, the time involved in producing two-piece interior upper constructions is significantly greater, so that the two-piece interior uppers are significantly more expensive to produce than one-piece interior uppers.